"It is difficult to say yet how much time they will take. There is an agreement between governments and now we are simply discussing the terms," Russia's official Tass News Agency quoted Rogozin as saying on the sidelines of Prime Minister Narendra Modi's ongoing visit to this Russian city.

India had announced on 15 October last year a deal on the Triumf air defence systems from Russia, worth over $5 billion, and collaborate in making four state of art frigates besides setting up a joint production facility for making Kamov helicopters.

The deals were announced following talks held between Modi and Russian president Vladimir Putin on the sidelines of the BRICS Summit held in Goa.

The S-400 Triumf long-range air defence missile system has the capability to destroy incoming hostile aircraft, missiles and even drones at ranges of up to 400 km.

India and Russia have been in talks for over a year for the purchase of at least five systems of S-400 that will be a game changer in the region.

It is capable of firing three types of missiles, creating a layered defence, and simultaneously engaging 36 targets.